The invention relates to a semiconductor device with an operating frequency above 50 MHz comprising a body composed of a soft ferrite material, said body having a surface to which a semiconductor element, a pattern of conductors and a passive element are fastened, which passive element is shaped like an inductor.
Such a semiconductor device can be used as a receiver for application in radio apparatus (about 100 MHz), television apparatus (about 450 to 860 MHz) and mobile telephone apparatus (about 900 MHz). In practice, the semiconductor device may comprise many active and passive elements, which active elements may be arranged in an integrated circuit comprising a very large number of transistors, and which passive elements may comprise besides one or several inductors, for example, capacitors and resistors.
A semiconductor device of the kind mentioned in the opening paragraph is known from published patent application WO 96/13858. The known semiconductor device is suitable for processing microwave signals and comprises a body composed of ferrite material, which body of ferrite material advantageously influences the performance of the inductor compared to a body composed of glass.
The performance of an inductor is often measured in terms of the quality factor Q, which is defined as the inductive reactance .omega.L, with .omega. being the angular frequency and L the inductance, divided by the total resistance R. From a theoretical article entitled "Planar inductors on magnetic substrates", written by Roshen and published in IEEE Transactions on Magnetics, Vol. 26, No. 1 (1990), pp. 270-275, it is known that the use of a magnetic carrier body might result in a 100 percent enhancement in inductance and, hence, in the quality factor of an inductor compared to a non-magnetic carrier body, provided that the magnetic carrier body has a magnetic permeability much larger than one.
As the quality factor Q of an inductor is proportional to the typical width (e.g. diameter) of the inductor, which may be, for instance, a substantially circular, square or rectangular spiral, a doubling of the quality factor can be turned into a saving in inductor surface area of approximately 75%. Considering a typical surface area of an inductor of the order of 1 mm.sup.2, it is evident that a saving of 75% in inductor surface area strongly influences the total number of semiconductor devices that can be manufactured per unit of surface area.
In order to attain the above-mentioned doubling of the quality factor of an inductor to be integrated in a semiconductor device with an operating frequency above 50 MHz, generally a soft ferrite material is selected which is capable of following the alternations of the magnetic field at the operating frequency of the semiconductor device. This is supported by the statement given in a standard textbook entitled "Soft ferrites: properties and applications", second edition, written by E. C. Snelling and published by Butterworths, London (1988), p. 90, that the useful frequency range of a ferrite is limited by the onset of ferromagnetic resonance, either because the permeability begins to fall or, at a somewhat lower frequency, the losses rise steeply.
A disadvantage of a semiconductor device of the type mentioned above, in which a soft ferrite material is applied which is capable of following the alternations of the magnetic field at the operating frequency of the semiconductor device, is that its manufacturing costs are high owing to the high initial costs of the soft ferrite material applied.